In U.S. Pat. No. 6,763,898 and WO02/18742, which are incorporated herein by reference, multiple firing line hoist systems to be mounted on the hull of a drilling vessel are disclosed. In general these known multiple firing line hoist systems comprise:                a mast having a top side and a base connected to the hull of the drilling vessel, wherein the mast has a hollow construction with a first side and an opposed second side,        a first hoisting device supported by the mast and having a load attachment device displaceable along a first firing line, which extends on the outside of and adjacent to the first side of the mast;        a second hoisting device supported by the mast and having a load attachment device displaceable along a second firing line, which extends on the outside of and adjacent to the second side of the mast.        
The first and second hoisting devices each include one or more cables and one or more associated winches, the winches preferably being disposed in the hollow construction of the mast, to manipulate the position of each of the load attachment devices relative to the mast.